This application is based upon and claims priority from Korean Patent Application No. 2001-0080015 filed Dec. 17, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor laser diodes, and more particularly, to a method of isolating semiconductor laser diodes by which laser emitting faces that are perpendicular to laser oscillation layers and have clear surfaces can be secured.
2. Description of the Related Art
A demand for semiconductor light-emitting diodes (LEDs) that emit light in the visible spectrum has increased with an increase in the necessity of high density information writing. As a result, semiconductor laser diodes (hereinafter, referred to as xe2x80x9cLDxe2x80x9d) of various types which emit lasers in the visible spectrum have appeared. Among them, a nitride semiconductor LD of an III-V group has attracted special attention because of its direct transfer method where a probability of a laser oscillation is high and its possible blue laser oscillation.
In general, to manufacture a semiconductor LD having a low threshold voltage and high power, the semiconductor LD has to be cut so that a laser emitting face of the semiconductor LD is perpendicular to an oscillation layer and has a clear surface.
In a process of cutting the semiconductor LD, the luminance of a laser is largely deteriorated and the laser scatters on the laser emitting face if the laser emitting face is not perpendicular to the oscillation layer and has a rough surface. In this case, both critical current and critical voltage of the semiconductor LD increase.
A method of isolating a semiconductor LD, which is related to the above-described cutting of the semiconductor LD, according to the prior art will be described with reference to FIGS. 1 and 2.
An n-type GaN-based compound semiconductor layer 4, a GaN-based active layer 6 from which a laser is generated, and a p-type GaN-based compound semiconductor layer 8 are sequentially formed on a sapphire substrate 2. A predetermined etching process forms a plurality of semiconductor LDs each having a ridge region 10 where p-type electrodes 16 are formed, a support 12, and an n-type electrode portion 14 where p-type electrodes 16 and an n-type electrodes 18 are formed. A base cut line necessary for isolating the semiconductor LDs is scribed on a portion of the bottom surface of the sapphire substrate 2. More precisely, the base cut line is scribed along a potential division line L for dividing the semiconductor LDs using a diamond tip. A semiconductor LD 22 having a laser emitting face 20 as shown in FIG. 2 is formed by applying pressure on the ridge region 10 over the potential division line L using a ceramic knife.
In the method of isolating the semiconductor LD according to the prior art, a step between an N electrode and a P electrode is high, and pressure has to be applied on the ridge region 10 over the potential division line L to cut a thick n-type compound semiconductor layer, an active layer from which a laser is emitted, and a p-type compound semiconductor layer. In this case, a laser emitting face is not formed along a major plane of the sapphire substrate, but the compound semiconductor layer is frequently cut along a major plane of the compound semiconductor layer formed on the sapphire substrate.
When the semiconductor LD on the sapphire substrate is cut along a crystal plane different from the major plane of the sapphire substrate, the length of an oscillator is changed and the laser emitting face is not perpendicular to a direction along which a laser has to be emitted. As a result, the emitting of laser deteriorates, and yield of a process of isolating the semiconductor LD reduces with a reduction in the reproduction rate of the semiconductor LD.
To solve the above-described problems, it is an object of the present invention to provide a method of isolating semiconductor LDs by which the semiconductor LDs can be cut by applying a small force, laser emitting faces that are perpendicular to directions along which lasers are emitted and have clear surfaces can be obtained, and the reproduction rate of the semiconductor LDs can be increased.
Accordingly, to achieve the above object, there is provided a method of isolating semiconductor laser diodes. A n-type compound semiconductor layer is formed on a substrate. A plurality of semiconductor laser diodes having the n-type compound semiconductor layer are formed on the n-type compound semiconductor layer so that laser emitting regions of the semiconductor laser diodes are connected to each other. The n-type compound semiconductor layer and a material layer of which the semiconductor laser diodes are formed are removed around the semiconductor laser diodes and the laser emitting regions for connecting the semiconductor laser diodes to each other. Base cut lines that perpendicularly cross the laser emitting regions are formed on backside of the substrate between the semiconductor laser diodes. The semiconductor laser diodes are isolated from each other along the respective base cut lines.
When forming the plurality of semiconductor laser diodes, a plurality of semiconductor laser diodes including a ridge portion having a stripe shape on the n-type compound semiconductor layer in the directions along which lasers are emitted and a p-type compound semiconductor layer having p-type electrodes on ridge parts of the ridge portion are formed.
When forming the plurality of semiconductor laser diodes, a plurality of semiconductor laser diodes having n-type electrodes on predetermined regions of the n-type compound semiconductor layer adjacent to the ridge portion are formed.
When forming the plurality of semiconductor laser diodes, a plurality of semiconductor laser diodes having supports for relieving stress occurring when the semiconductor laser diodes are packaged are formed on predetermined regions spaced apart from the ridge portion of the p-type compound semiconductor layer.
The active layer is an InXAlYGa1xe2x88x92Xxe2x88x92YN layer, where 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61 and x+yxe2x89xa61 or an InXAlYGa1xe2x88x92Xxe2x88x92YN layer having a multi quantum well structure.
When removing the n-type compound semiconductor layer and the material layer of which the semiconductor laser diodes are formed, first, a mask, which covers the plurality of semiconductor laser diodes and portions for connecting the plurality of semiconductor laser diodes to each other in the directions along which the lasers are emitted, is formed on the resultant structure obtained from the formation of the plurality of the semiconductor laser diodes. Next, the resultant structure on which the mask is formed is etched until the substrate is exposed, and then the mask is removed.
Using the present invention, a laser emitting faces of the semiconductor LDs, which are perpendicular to directions along which laser are emitted and have clear surfaces, can be obtained. As a result, reproduction rate of semiconductor LDs are increased, which considerably reduces frequency of cutting the laser emitting faces of the semiconductor LDs in opposite directions to the cut face of the substrate in a repetitive process of isolating the semiconductor LDs. In other words, failure can be minimized in the process of the isolating the semiconductor LDs.